After many years of thinking about it, I've finally decided to build an AR. I'm mainly a pistol shooter and don't own an AR. I have an Aero M4E1 lower and their Enhanced complete upper on order. I'm leaning toward the Toolcraft NiB BCG. My question is, how many of you would disassemble their new complete upper and BCG to check headspace and make sure the barrel nut has properly seated and torqued? I consider myself above average in gunsmithing skills, but don't want to waste my time if it's not necessary. Thanks.

Take the big apart. Sure. Check headspace if you like (99% its fine). I wouldn't go further unless there was a problem when shooting it. If I wanted to torque a barrel nut I'd build the whole thing vs. buy a complete upper.

You're wasting your time, but have fun.

It was much cheaper to buy the assembled upper than the individual parts. I'm trying to avoid problems down the road. I've seen too many things that you can't take apart without destroying due to shortcuts on assembly. And as a lefty, I'd like to avoid a blowout to the face.

Sounds like you had your answer before you posted. Have fun.

I might check headspace.  Where are you getting the complete upper?  If you can’t trust that the barrel is installed properly then I’d suggest buying from a more reputable company.

I always check everything well to start with before I shoot it.
I generally end up changing everything around over time and do a more extensive job as I change things. I doubt any factory upper is given the thorough installation of parts I would do myself.

I would disassemble the bolt carrier assembly to inspect, clean and oil it.

You don't have to remove the barrel to check the headspace.  You do need to disassemble the bolt (for Forster gauges anyway).

When I've bought assembled uppers I never worried about the barrel nut torque (bit me once, a long time ago, when I bought an upper from a company thoroughly hated/looked down on here and before I knew better - have not bought from them since.)

I disassemble the BCG to at least make sure gap on the gas rings are evenly spaced, and to provide some initial lubrication, light oil to the carrier bore where the gas rings slide, and some moly grease to the bolt cam area.

BCG is good to disassemble for cleaning.

If you're gonna pull the barrel and re-torque the nut might as well just build your own upper in the first place.

Clean the BCG, swab the bore till patches come out clean, go shoot it.  If there are issues, *THEN* worry about barrel nut torque.  (or send it back to the retailer to replace/repair on their own time).

Clean the snot out of everything before you assemble it.  That doesn't mean you need to tear down the assemblies to the smallest parts, but a BCG should be completely disassembled, then thoroughly degreased before you start.  Likewise LPKs: degrease everything before you start your build.

Parts and assemblies are usually not coated with "lubricant."  They're coated with something that will keep them from rusting or discoloring while they are stored.  Removing that crap is important because it "kinda looks like" a lubricant, but it will get in the way of a real lube.

I soak LPK parts in oil after degreasing them, but I just do a good "deep cleaning" of assemblies like BCGs.  But EVERYTHING gets thoroughly cleaned before it gets near being assembled.

I always check headspace.
Bolts have a tolerance range of .003” which is why a person should check headspace with the bolt that will be used with the barrel.
A friend bought 3 assembled uppers at the same time; all 3 failed the Go gage.
I also like to run a pipe cleaner in the ejector hole, as I occasionally find some grit or something there in new bolts.